Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
  • C22C5/02—Alloys based on gold
• • A—HUMAN NECESSITIES
  • A44—HABERDASHERY; JEWELLERY
  • A44C—PERSONAL ADORNMENTS, e.g. JEWELLERY; COINS
  • A44C27/00—Making jewellery or other personal adornments
  • A44C27/001—Materials for manufacturing jewellery
  • A44C27/002—Metallic materials
  • A44C27/003—Metallic alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C28/00—Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/14—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of noble metals or alloys based thereon

Definitions

• the present invention relates to an alloy based on gold and aluminum, useful in particular in the field of jewelry or watchmaking, and having a violet tint.
• Alloys of this type are known, including the gold alloy commonly called “purple gold". It is an alloy composed of 78.5% by mass of gold and 21.5% by mass of aluminum and which contains crystallographic phases which gives it a violet colour. In particular, the presence of the AuAl 2 intermetallic phase obtained following the melting of the alloy is known as conferring the violet color on the alloy.
• An object of the present invention is to provide a gold-based alloy which retains the aesthetic interest of violet gold, but improving its mechanical properties, in particular with a view to shaping it, for example by machining or for improve its durability by increasing its breaking strength and more generally to broaden its possibilities of use.
• the invention aims in particular to provide an alloy having a violet shade of the same type as that of violet gold, with a caratage preferably of at least 18 carats (namely comprising at least 75% by weight of pure gold).
• the present invention proposes a new type of alloy, based on gold and aluminum, and further comprising at least two addition elements in addition to gold and aluminum, whose inventors have now demonstrated that it has much more interesting mechanical properties than violet gold, and in particular excellent impact resistance, while retaining aesthetically interesting violet nuances.
• the alloy of the invention may optionally comprise additional elements other than the first and the second additional element defined above.
• the alloy may comprise the first additional element (Si or Sn); the second additional element distinct from the first and chosen from Si, Sn, Pd, Pt, Ag, and Cu; and a third additional element distinct from the other two, chosen from Si, Sn, Pd, Pt, Ag, and Cu.
• the alloy may comprise, in addition to the first and at least second additional elements, another element distinct from Si, Sn, Pd, Pt, Ag, and Cu, for example traces of oxygen.
• the alloy can also include impurities (in general height of less than 0.2% by mass and more preferably less than 0.1% by mass).
• the alloy of the invention constitutes an alloy which is similar to violet gold, in particular by its high gold content which makes it a precious alloy. It comprises at least 75% gold, this percentage being expressed in mass relative to the total mass of the alloy, which corresponds to a caratage of at least 18 carats for the alloy.
• the gold content is between 75% and 85%, and for example between 75% and 78% by mass relative to the total mass of the alloy.
• the alloy has a caratage of 18 carats, with a gold content equal to or slightly greater than 75% by mass relative to the total mass of the alloy.
• the aluminum content is less than 25%, preferably between 12% and 24%, for example between 16% and 21% by mass relative to the total mass of the alloy.
• the aluminum content in the alloy may be between 16% and 19% by mass relative to the mass total alloy.
• the alloy according to the invention comprises at least two additional elements chosen from Si, Sn, Pd, Pt, Ag, and Cu with at least Si or Sn present.
• the total content of Si, Sn, Pd, Pt, Ag, and Cu elements in the alloy is less than 15%, preferably between 1% and 13%, for example between 4% and 8% by mass relative to the total mass of the alloy.
• the content of the first additional element, chosen from Si and Sn, is between 0.1% and 6%.
• silicon (Si) When silicon (Si) is present as an additional element in the alloy, its content is preferably less than 4%, for example from 0.1% to 3%, in particular from 0.1% to 2% in mass relative to the total mass of the alloy. This is in particular the case when silicon is present as the first additional element. In this case, the total content of the other additional elements is in complementary proportion with respect to the total mass of the alloy.
• the second additional element can, according to an advantageous embodiment, be chosen from palladium (Pd); platinum (Pt); silver (Ag), and copper (Cu), and this second element is then present in the alloy at a content ranging for example from 4 to 6% by mass relative to the total mass of the alloy.
• tin (Sn) When included as an additional element in the alloy, it is preferably present at a rate of 0.1% to 6%, for example between 2 and 6%, by mass relative to the total mass. of the alloy. This is in particular the case when tin is present as the first additional element. In this case, the total content of the other additional elements is in a complementary proportion by mass relative to the total mass of the alloy.
• the second additional element can, according to an advantageous embodiment, be chosen from platinum (Pt) and silver (Ag), and this second element is then present in the alloy at a content ranging for example from 2 to 6% by mass relative to the total mass of the alloy.
• the alloy of the invention comprises both silicon (Si) and tin and (Sn).
• each of Si and Sn can be considered as the first or a second additional element.
• the silicon content is preferably less than 4%, more preferably between 1.5 and 2.5%, for example 2%, by mass relative to the total mass of the alloy and the content pewter is preferably between 2 and 6% by mass relative to the total mass of the alloy.
• the alloy contains both silicon (Si) and tin (Sn)
• it may comprise an additional third element preferably chosen, where appropriate, from Pd, Pt, Ag, Cu, and Mn, and this third element is preferably platinum (Pt) or palladium (Pd).
• an alloy according to the invention is obtained by a preparation process which comprises (i) the melting of the various constituents of the alloy in the metallic state (isolated or in the form of pre-alloys) in the proportions of the alloy whose synthesis is desired, whereby a mixture of the constituent elements of the alloy in the molten state is obtained, then (ii) cooling of the mixture obtained which leads to obtaining the desired alloy.
• This method of preparation constitutes, according to another aspect, another object of the present invention.
• An alloy according to the invention can also be obtained by a process comprising (i) powdering the constituent elements of the alloy or a pre-alloy by crushing or preferably by atomization, (ii) mixing and homogenizing the powder in the case where the alloy elements are powdered separately and (iii) a sintering step, for example by Laser or preferably by SPS (Spark Plasma Sintering).
• a sintering step for example by Laser or preferably by SPS (Spark Plasma Sintering).
• the alloys according to the invention With the alloys according to the invention, problems similar to those encountered with violet gold can be encountered even if these are reduced.
• the solidification of the molten mixture is likely to form porosities, for example of the micro-resintage type, which are at least partly the cause of the fragility observed for violet gold.
• the composition of the alloys of the invention already makes it possible in itself to limit the formation of this type of porosity, but, to reduce them further, it is interesting to play on the process parameters.
• an alloy according to the invention can in particular be obtained by progressively cooling the liquid mixture comprising the constituents of the alloy in the proportions of the final alloy.
• This liquid mixture can in particular be obtained by melting (for example within a crucible) shot, plates or other solid elements. comprising the elements of the desired alloy within a suitable heating device (induction furnace for example, or arc furnace).
• the liquid mixture comprising the constituents of the alloy in the proportions of the final alloy is then cooled to form the final alloy.
• the final alloy can in particular be cast in an ingot mold.
• the ingot mold can advantageously be preheated before the mixture is poured into it.
• their method of obtaining can advantageously comprise a heat treatment step following the cooling of step (ii).
• This heat treatment which induces a relaxation of the material and therefore a reduction in its internal stresses, which further increases its mechanical performance and in particular its ductility.
• the alloys obtained within the scope of the invention have an advantageous violet coloring associated with advantageous mechanical properties, in particular in terms of impact resistance.
• the alloys according to the invention can resist a ball drop, as defined for example according to the ISO 14368-3 standard, advantageously from a height of at least 5 cm, preferentially from a height of at least 10 cm, and even more preferably with a height of at least 20 cm.
• an alloy having the aforementioned Composition 5 (comprising 2% Si and 6% Pt) resists, under the conditions of standard ISO 14368-3, a ball falling from a height of 27 cm.
• an alloy having the aforementioned Composition 8 (comprising 2% Si and 6% Ag) resists, under the conditions of standard ISO 14368-3, a ball falling from a height of 33 cm.
• the test referred to herein is a cumulative test, with the samples tested being progressively subjected to ball drop tests with increasing drop heights.
• an alloy according to the invention is more resistant to corrosion, that is to say that the time to observe a deterioration of the alloy, for example by a pitting phenomenon, when it is placed in a corrosive environment , for example salt spray or moist heat, and longer than with violet gold known from the prior art.
• the alloys of the invention can be used as constituent materials of all or part of luxury items including, without limitation, items of jewelry or watches, writing instruments, luggage and belt buckles as well as leather goods accessories. These various uses constitute yet another object of the present invention.
• the invention also relates to the above-mentioned luxury articles comprising at least one part consisting of an alloy according to the invention.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Powder Metallurgy (AREA)
• Adornments (AREA)

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• 2021
  • 2021-03-01 EP EP21305245.9A patent/EP4053299A1/de active Pending
• 2022
  • 2022-02-25 EP EP22159005.2A patent/EP4053300A1/de active Pending

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